1. Field of the Invention
The present invention relates to a structure for holding an image sensor used to read an original in a facsimile terminal and more particularly to such a structure possessed by the image sensor itself so as to mount its light receiving sensor substrate on a frame (in the main body of the image sensor).
2. Description of the Related Art
FIG. 4 is a cross-sectional view of the primary part of an image sensor constructed according to the prior art, taken along a plane perpendicular to the direction of scan. The image sensor comprises a light source unit 4 for illuminating an original A, a light receiving sensor 5 including a plurality of light receiving portions arranged therein, and an optical system 6 for causing the light from the original A to be received on the light receiving portions in the light receiving sensor 5, these components being mounted in a frame 1. The light source unit 4 includes a resilient element 44 which will be brought into contact with the optical system 6 under pressure when the resilient element 44 is resiliently deflected. The optical system will be fixedly pressed against a wall 1a in the frame 1. Further, the light source unit 4 itself is resiliently biased against a wall 1b in the frame 1.
The light source unit 4 comprises an LED chip 42 die bonded on a substrate 41 and a plastic lens 43. Light emitted from the light source unit 4 is adapted to illuminate a transparent glass plate 7 located on the top of the frame, that is, the original A placed thereon with an angle of about 45 degrees. Light reflected by the original A is received by the light receiving sensor 5 (which is a photodiode array chip die bonded on a substrate 3) located on the bottom of the frame through the optical system 6 which is a refractive index gradient type lens array. The light receiving sensor 5 converts the received light into an electric signal.
In such a prior art image sensor, the light receiving sensor substrate 3 is positioned in contact with the bottom face of the frame 1 and fixed to the frame 1 by means of machined screws 8. In general, the material of the image sensor frame 1 (which is usually of aluminum alloy or plastic) is different from that of the light receiving sensor substrate 3, naturally leading to a difference of thermal expansion coefficient. When the substrate 3 screwed to the frame 1 expands or contracts due to change of temperature, the substrate 3 may be deformed at a position between any adjacent machined screws 8, that is, at any portion not held by the machined screws. The use of the machined screws requires the machining of threaded apertures both in the frame and substrate 1, 3 and renders the mounting operation troublesome, leading to an increase in the manufacturing cost.